The present invention relates to an alarm system, and more particularly, to a fire alarm system in which groups of addressable terminal units are connected to respective transmission loops, synchronous power and serial data transmission being effectuated over such loops.
The arrangement or scheme in accordance with the present invention may be appreciated in connection with the complete fire alarm system disclosed in related applications ED-244 and ED-246, the details of which are incorporated herein by reference. In both of those applications, the particular relationship between the loop controller, described herein for controlling a given loop or line, and the master controller, which controls all aspects of the system, will be apparent. It will be especially appreciated that when data is sent back to the loop controller discussed herein, it is further transmitted, in accordance with the complete system of the two related applications, to a master controller so that indications can be given at a central control panel of the conditions existing at all of the detectors, sensors, and devices of various other types included in all the loops forming the system. The master controller is operative to generate an audible alarm, and a display, at the control panel to alert personnel at that central location when terminal units are in alarm or there is trouble anywhere in the system, and further to cause a print record to be made of such conditions.
It is desirable at the same time to indicate at a particular terminal unit that such unit is in an alarm state so that supervisory personnel can pinpoint that location and hence be able to take remedial action.
However, a significant difficulty occurs in the event that a large number of terminal units go into the alarm state. One form of terminal unit includes a new-style, completely addressable, analog detector which is packaged with a "chip" or "chips" embodying components such as an address comparator, an A to D convertor, a command discriminator, etc. In this connection, reference can be made to U.S. Pat. No. 4,581,604 for a description of this type of terminal unit.
The detectors of such terminal units can be accessed in a cyclical manner, such as by a so-called polling routine; data on the state of the detector can then be sent back to a loop controller, and commands given to the terminal unit by that loop controller. The term transponder, as used in the current description, refers to a form of terminal unit like the first, except that conventional "slave" detectors, or other initiating devices, are connected to the chip, the transponder being accessed in the same manner as a terminal unit featuring the new-style analog detector. The slave detectors, or other initiating devices, however, are not individually addressable.
The difficulty already referred to is that when a large number of terminal units are in the alarm state, an unacceptably high power drain is involved. For example, since conventional detectors used in connection with a transponder individually draw approximately 15 milliamps, it is intolerable to have more than one of these indicating its alarm state because, in that situation, excessive power would be consumed.
Accordingly, it is a principal object of the present invention to conserve power consumption on a loop when any type of terminal units go into alarm. To this end, significant power savings are obtained by disconnecting the slave initiating devices of the type of unit defined above as a transponder after the central panel has already latched the alarm state indication from that transponder.
Another goal or object is always to allow every terminal unit to indicate an alarm state. Heretofore, it had become the practice to illuminate the light emitting devices of the first ten units when they come into alarm. However, this has been found to be unsatisfactory because, as currently designed, transponders located on the loop still draw their 15 milliamps of alarm current.